1. Field of the Invention
This invention relates to trailers, and, more particularly, to telescoping boat trailers.
2. Description of the Prior Art
As is well known and understood, boats are typically launched from ramps which extend into bodies of water, such as lakes, rivers, etc. In order to launch boats conveniently, it is required that the trailer on which the boat is disposed be extended far enough into the water to float the boat upon its release from the trailer. An inherent difficulty arises when a car or truck is unable to place the trailer sufficiently in the water to float the boat because of the danger of water damage to the vehicle. An obvious answer to such problem is to provide an extensible trailer with the portion supporting the boat movable relative to a fixed portion secured to the vehicle.
Typically, extensible trailers use telescoping frame members with the inner frame member secured to the vehicle and an outer portion movable relative to the inner member and thus extensible into the water and to a depth, hopefully, that will allow the boat to be conveniently released from the trailer and launched on the water.
For moving one portion of the trailer relative to the other portion of the trailer, there have been several different types of mechanical arrangements suggested. One type of arrangement is a cable arrangement using either a hand cranked winch or a motor actuated winch. However, there have been a number of trailers which utilize electrical motors and a positive engagement between the two portions on the trailer. Some type of grate system is preferred for this type of system. The prior art discloses a typical rack and pinion type drive or actuation system.
U.S. Pat. No. 2,894,766 (Habriga) discloses an extensible tongue and hitch between a tractor and a trailer. Movement of the trailer relative to the tractor is accomplished through a rack and pinion connection. The rack comprises the fixed, internal portion of the hitch apparatus, and a pinion gear is secured to the outer portion of the hitch and to the trailer, and is rotated by a hand crank to move the trailer relative to the tractor.
U.S. Pat. No. 3,032,353 (Williams et al) discloses a telescopic tow bar for a boat trailer. Relative motion between the telescoping members is accomplished by the use of compressed air or the like. The inner element acts as a piston rod, and the outer element, which moves relative to the inner element, acts as a cylinder. Compressed air introduced on opposite sides of the piston causes movement of the cylinder, and the boat trailer, relative to the piston and its associated fixed elements.
An obvious disadvantage of the apparatus of the '353 patent is in the cost of providing and maintaining a sealed relationship between the relative moving members. Also, the requirement of providing compressed air and the required hoses and valves is another obvious problem.
U.S. Pat. No. 3,083,986 (Moody et al) discloses a boat trailer with relatively movable telescoping elements. Internal roller elements are journaled on the inner, fixed element to provide bearing surfaces for the outer, movable members. A cable and winch system is used to provide relative motion between the fixed and movable portions of the apparatus. The provision of rolling elements secured to the inner, fixed element, provides inherent cost problems. Moreover, the more the trailer is extended, the less rigid it becomes.
U.S. Pat. No. 3,102,737 (Williams et al) discloses details of a pressure equalizer system usable with apparatus similar to that disclosed in the '353 patent. It will be noted that the inventors of the '353 patent and the '737 patent are the same. In addition, some of the drawings are substantially the same.
A piston and cylinder action, using compressed air, provides the actuation for the relative moving elements.
U.S. Pat. No. 3,984,121 (Dobosi) discloses a telescoping boat trailer system utilizing a rack and pinion system. The rack and pinion system is hand cranked.
U.S. Pat. No. 3,989,266 (Foster) discloses another boat trailer system in which telescoping action between relatively movable elements is provided through a chain drive. The chain drive is disposed within the interior, fixed member, while the outer, relatively movable, member includes a follower secured to the chain. A slot extends through the inner member to provide a connection between the follower and the chain. Chains require substantially constant maintenance, and the maintenance may be a problem when the chain is disposed within a member, as in this Foster patent.
An obvious disadvantage of the apparatus of the '266 patent is the cost involved in the chain drive and in the machining of the slot.
U.S. Pat. No. 4,169,611 (Smith et al) discloses another extensible trailer system in which an outer sleeve is movable relative to an inner element. Relative movement is provided through a rack and pinion drive. Two embodiments are shown, only one of which includes the rack and pinion drive. In the other embodiment, there is no mechanical drive system disclosed.
An obvious problem with all of the systems utilizing rack and pinion drive is the cost involved. The machining required for racks, particularly of the length involved in boat trailers, is relatively high, and thus the cost of the trailer is relatively high. In addition, the rack is generally disposed either within, or as, the interior element, and it is accordingly required to completely separate the relatively movable portions (the telescoping portions) in order to perform any maintenance or repair work on the rack.